1. Technical Field
The present invention relates to a power transfer system for use in a motor vehicle, and more specifically to a power-interrupt auto-manual transmission having means for providing power to the output side of the transmission during the shifting of the transmission.
2. Discussion
Over the past two decades, vehicle manufacturers have made enormous efforts to improve fuel economy and reduce exhaust emissions. The principal commercially acceptable source of these improvements has been in the area of engine combustion technology; improvements in the area of power transfer systems have generally not yielded much commercial success due to the consumer preference for the automatic transmission.
Automatic transmissions incorporating torque converters, epicyclic gear trains and hydraulic pumps represent a high degree of sophistication in response to changing vehicle speed, engine speed and operator commands. As such, automatic transmissions have gained wide acceptance in automobiles and light trucks despite their failure to achieve throughput efficiency as high as an equivalent manual transmission. In operation, this lower efficiency manifests itself as higher fuel consumption by a vehicle equipped with an automatic transmission than a comparable vehicle equipped with a manual transmission. In passenger cars where convenience is a major consideration, a fuel consumption penalty of five to ten percent is generally tolerated.
One prior art solution, known as the power-interrupt auto-manual transmission, has been a power transfer system having a conventional manual transmission coupled with means for shifting the transmission automatically. In operation, the shifting means monitors a number of vehicle dynamics, including vehicle speed and engine speed, and performs a shift in response to these dynamics according to a predetermined algorithm. To perform a shift, the shifting means interrupts the supply of power to the transmission by disengaging a clutch, selects the desired gear stack and then engages the clutch to actuate the new gear stack. The shifting means essentially removes the need for human interaction from the shifting of a manual transmission, allowing shifts to be performed under optimal conditions. As such, improved fuel economy is provided even when compared against a completely manual transmission. Power-interrupt auto-manual transmissions also have the advantage of being generally less complex and less costly than a comparable automatic transmission or other auto-manual transmission types, such as the preselector type.
However, in spite of these advantages, power-interrupt auto-manual transmissions have not met with widespread commercial success as a result of the transmission shift characteristics. These characteristics include a number of subjective and objective criteria, but most significantly include the sensation of "no power" experienced by the vehicle operator during a shift and the overall cycle time of the shift.
The sensation of "no power" is created when the shifting means interrupts the supply of drive torque to the transmission during a shift and as such, the potential for this sensation is not unique to power-interrupt auto-manual transmissions. However, operators of vehicles equipped with manual transmissions are distracted by the manual operation of the clutch and gear selector and consequently do not develop the sensation of "no power." Although the shifting cycle of an automatic transmission or a preselector auto-manual transmission is comparable with that of a power-interrupt auto-manual transmission, the automatic and preselector transmissions are able to engage two gearsets during at least a portion of the shifting cycle which thereby eliminates the sensation of "no power" experienced by the vehicle operator. Although advancements in logic controls and electro-mechanical actuators offer some promise of reducing the overall cycle time of the shift of a power-interrupt auto-manual transmission, it is unlikely that the cycle time could be shortened enough to eliminate the sensations of "no power" due to the fundamental differences in the gear shifting mechanics between automatic and power-interrupt auto-manual transmissions.
Another matter impeding the commercial acceptance of power-interrupt auto-manual transmissions concerns the fueling of the vehicle engine during a shift. During the power-interrupt portion of the shift, the throttle controls of the prior art power-interrupt auto-manual transmissions typically reduce the fuel supplied to the engine, causing the engine to decelerate during the shift. The engine is therefore decelerated at the beginning of the shifting cycle when power to the transmission is interrupted and accelerated at the end of the shifting cycle to match the engine speed to the speed of the transmission. As such, the exhaust emissions output of the vehicle is negatively impacted as a result of the deceleration and acceleration that accompanies every shift.
Consequently, there remains a need in the art for a power-interrupt auto-manual transmission that substantially eliminates the sensation of "no power" experienced by the vehicle operator during a shift. There also remains a need in the art for a power-interrupt auto-manual transmission with improved throttle controls to reduce exhaust emissions of the engine produced during the shifting cycle.